Three months ago, I refreshed my firefighting skills in a class created by the National Wildfire Coordinating Group. I spent most of my week alone in front of a computer, clicking through various lessons that have been digitized since the last time I took the course more than 10 years ago.

One new lesson explained what to do if I encountered a meth lab. Another went over how to identify hazardous waste and chemicals if I happened to stumble upon an illegal dump. I could only shake my head. The last time I worked on a fire line such hazards were far from my mind.

But these are the least of the changes complicating the job for today’s firefighters, who suffered the worst U.S. wildfire disaster in 80 years last week, when 19 died in Yarnell, Ariz.

When I last trained to fight wildfires, climate change was far from most firefighters’ minds. Today, it’s hard to find a veteran firefighter who hasn’t seen firsthand the warming and drying of the nation’s forests and how that’s increasing the intensity and frequency of fires.

The first fire I covered last year in my home state of Colorado was in the waning days of winter, when the forest is normally covered in snow. “We’re seeing fire behaviors we’ve never seen before,” an incident commander told me.

Officials have since repeated that phrase like a mantra. I heard it again that March at a prescribed burn, a fire intentionally set by the Colorado State Forest Service to improve the forest’s health. It spread into an adjacent neighborhood and destroyed 23 homes, killing three residents.

I heard the phrase later at fires outside Fort Collins and Colorado Springs that destroyed more than 600 homes. I heard it again last fall at a fire in Rocky Mountain National Park that burned through the winter.

Colorado has broken its “most destructive fire” record four times in the last four years. By many measures Arizona, where the Granite Mountain Hotshots died, has it even worse.

According to research by Climate Central, Arizona is warming faster than any other state in the U.S., with temperatures increasing by 0.72 degrees a decade since the 1970s. That warming has brought with it more frequent, severe and long-lasting droughts.

The warming and drying of the Southwest aren’t the only reasons fires now burn bigger, faster and hotter. Historically every few decades wildfires consumed the dead wood and grass, small trees and brush crowding the forest. During the past century, land managers have successfully put out more than 98 percent of the fires in Arizona forests, leaving natural fuel that would have otherwise burned away.

This week, Congress will hold hearings about how to thin the overgrown forests. It is unlikely to make progress. The cost of physically clearing out excess timber and brush from forests is high, and so is the public resistance to controlled-burning programs. Timber harvests and grazing, a priority for many Western legislators, can reduce some fire hazards but often make others worse.

The greatest challenge to firefighters may not be the trees or the tinder, which have always been there, but the people. Last year I worked on a project to analyze development patterns in the “wildland urban interface,” where homes and human development abut flammable landscapes. In Colorado, we found that from 2000 to 2010, more than 100,000 people moved into the state’s “red zone,” land bordering the most flammable forests.

Today, more than one in five Colorado residents risk losing their home or their life to wildfire simply because of where they choose to live.

That population brings with it new fuels to the forest — houses, cars, piles of firewood and propane tanks. More significant, the people introduce new sources of ignition. Power lines can arc or snap when overburdened during heat waves. Vehicles and machinery spark hundreds of wildfires every year. Bullets from sportsmen’s guns and, in a few documented cases, sparks from golfers’ clubs striking rocks have ignited fires.

Wildland firefighters face increasing demand to protect these homes and communities. That’s a job they are far less equipped for than their urban counterparts. Wildfire crews wear lightweight flame-retardant clothes rather than heavy fire coats, pants and oxygen equipment. They usually have only an ax, shovel or chainsaw to fight the fire, rather than a ladder truck with thousands of gallons of water.

Nonetheless, it’s far harder to step back from a threatened home than it is a stand of trees.

In the 1990s the average cost to the federal government of preventing, preparing for and fighting wildfires was less than $1 billion annually, according to Headwater Economics. In the last 10 years, the cost has surpassed $3 billion.

Yet these costs pale when compared with the price paid by Prescott, Ariz., last week. Of the hundreds of Hotshot crews, the Navy SEALs of wildfire fighting, the Granite Mountain group is the only one that’s part of an urban fire department. Most of its members were born and raised in Prescott. When the Yarnell Hill fire broke out just 30 miles away, the proximity drove them to respond with even more urgency than they usually did. Some raced out so fast that, hours later, the meals they were halfway through were still sitting on the firehouse table.

They were among the best-trained forest firefighters in the world, yet of the 20 men who marched into the fire, only one — the lookout — survived. Officials said those who died were defending Glen Ilah, a subdivision outside Yarnell.

The investigation into the Hotshots’ deaths will go on for months, and there will probably be changes to the rules that govern how we fight wildfires. But with the homes, drug labs, hidden marijuana fields and dead wood increasingly filling our forests, and the climate-warming pollutants we continue to emit into the atmosphere, it’s hard to imagine how our safety protocols will ever keep pace with the hazard.

The only way to prevent the loss of firefighters in the forest is to not have them there at all. And, increasingly, even when homes and infrastructure are threatened, leaders of these fire fights have to make the right call — ordering firefighters to stand down from dangerous situations even when private property will burn.

Michael Kodas is an author and journalist. His latest book “Megafire” will be released next year.

Many were not surprised by the prompt verdict Monday in the sexual-assault case in Denver involving Taylor Swift. A jury of six women and two men concluded within hours that a Denver radio host had groped Swift _ grabbed her butt beneath her skirt during a photo shoot, as his wife stood on the other side of Swift.

Touch not that statue of Robert E. Lee in Charlottesville. Let it stand, but around it place plaques telling the curious that the man was a traitor to his country who went to war so white people could continue to own black people.